Mealy Bugs and how to handle team

Mealy Bugs and how to deal with them.

Learning to read your plants is a fantastic skill to have as an orchid grower and one that comes with time and experience. The ability to spot a problem before it becomes a major issue can save you much heartache. We recommend having a brief look at your plants nearly every day to check that things are OK. We look for bulb shrivel, marks on the leaves, insect damage, spikes appearing (always a joy), and new root tips to tell me when to repot.

 

Making a Meal out of Mealy Bugs

Contrary to popular understanding, we are not just talking about one bug here! 

It is in fact a group of bugs, in which we mostly find a number of fluffy, somewhat mealy, bugs - but also winged bugs like white fly (yes, it belongs in that group, too!). As with most Pests and Diseases, these annoying

little bugs have a cycle. For the most part you will notice an infestation with Mealybugs when you see the white and mostly already fluffy adults. The adults are covered in a white, waxy secretion, which is produced through their glands. The more the adult matures, the longer the threads will grow…occasionally very long at the body’s hind.

However, some type of Mealybugs only produce a powdery protection shield. When it comes to the reproduction cycle, by and large, Mealybugs usually lay eggs; but in favourable conditions, some species turn mainly viviparous and reproduce through pathogenesis. Meaning there are only female Mealybugs which only reproduce asexually. This way the reproduction cycle is much quicker than going through fertilisation and eggs. Yes, you’re right, it is a bug conspiracy!

Most commonly there are two species that occur on Orchids, first up; the most frequent visitor …

The long-tailed Mealybug 

The long-tailed Mealybug is easy to distinguish from other Mealybugs. It is usually approx 3 to 5mm long by the time you able to spot it. The body, when squashed, is reddish to orange and, of course, it comes with the characteristic long tail. The long threads or filaments are about as long as the body itself.

You sometimes start spotting that the leaf surface is looking shiny and sticky, take a look underneath the leaves and if there is a visible Mealybug population turning up, you will already have several different stages of the bug living in your plant. A single adult Mealybug can live up to two months.

 There are almost no male Mealybugs as this type of Mealybug is predominantly ovoviviparous (the small larvae develops inside the mother’s body and a living larvae - the first instar*/nymph - is then released). Male Mealybugs would more likely occur if there’s a recurring frost or drop in temperature to winter like conditions, in response to the bugs’ need to ensure the population will survive over the frosty winter.

It is one of the very resistant mealybugs, when it comes to insecticides. So if you wanted to take a sustainable route by using biological plant protection, it is vital to determine exactly the species you’re dealing with, as especially some parasitic wasps only feed on certain mealybug species.

Optimum conditions for the development of these predatory species are temperatures above 26°C with a higher humidity. Other than that there’s a good dozen of parasitic Wasps that prey on Mealybugs. Lacewings can feed on Mealybugs too, but the Nymphs are more after the juicy crawlers and as maturing on the first instar. There are companies in NZ that sell predator species… have a browse, it’s a Jurassic Park out there.

 

Citrus Mealybug

The second Mealybug to look out for is the Citrus Mealybug, this is easily spotted as a fluffy carpet like layer underside the leaves. Inside (and sometimes on top) of this fluff you see their yellow eggs. For the most part you will see this variety laying eggs, as the preferable temperature is 24°C or above for the females to become viviparous (when a mother develops a live young, rather than develop from an egg). If you see unevenly, blurred, yellowing blotches occurring on your orchids, have look under the leaf and you might spot the fluffy carpet that wipes away easily, leaving a somewhat mushy, fluffy yellow greenish white smear on your fingers. In general, these bugs cause damage on underside of the delicate leaves, and therefore inhibit the plants ability to properly complete photosynthesis and also have an impact on the plants metabolism; because of this damage you soon may get secondary bacterial or fungal infections. The sticky leaves are also indicative of their droppings which can also create an ideal breeding ground for fungus and bacteria

Now if you’ve ever been asking yourself; “Why do bugs seem to always sit under the leaves or at the fresh flower buds and spikes?” The answer is that in a plant there’s two types of sap, pretty much like you have veins and arteries, the plant is having a low energy sap coming from the roots and going up to the upside of a leaf. This sap is called xylem sap and is like your blood, that runs in the veins. After the photosynthesis, the now very rich sap is running back at the underside of the leaf and going down into the deeper system of the Plant to be used or stored elsewhere.

The sap that’s rich on sugary content, enzymes and hormones is than called phloem, therefore most bugs like the candy side of their plant hosts and so most horticulturists call them phloem sucker. 

Mealy Development.

For those of you interested the life cycle of mealybugs (to better understand how infestations occur), the first larval stadium* is tiny and almost never been seen with your bare eyes. You might potentially spot tiny little greenish spots on very dark Orchid flowers. Those first stage larvae are so called “crawlers” and they spread quickly as well as hiding in the smallest cavity, sometimes reinfesting a plant from so tight closed sheds or buds, where not even a non-systemic spray can reach.

Shortly after, the young crawler starts to feed on the sap, it starts to transform into a second instar** and it is then that it starts to cover their body with the white wax like cover, which gives them the mealy appearance. After a while it will transform into a third instar, even bigger and with a further transformation when it becomes an adult female.

You can still see them moving about as adults, especially if you poke at them to check if they’re alive. But by and large the crawler stadium is by far the most mobile one. In temperatures of 25°C - 27°C it takes about 30 to 35 days until the second instar becomes visible. If the temperatures aren’t optimal, the mealybug might develop into the winged third instar. This winged instar doesn’t feed anymore and solely interested in reproduction. In general there are always more females than males if the temperatures are under 27°C; above that temperature and the population splits more equally. If the temperatures rise above 35°C the mealybugs usually die, but would lay eggs beforehand to ensure the next generation.

Male mealybugs look a lot like a fungus gnats (see above image) and live for three days only as they do not have a rostrum or stylet to allow feeding, however they can mate with up to twenty females during this short time.

Female mealybugs can lay up to 300 eggs in their life, at approximately twenty eggs a day. While the reproduction through crawlers is a lot slower, it helps the pest to spread more wildly, as adult females die shortly after giving birth or laying eggs. While they drain the plant of its sap for their , meals… mealybugs in general create more damage through their excreted honeydew and the subsequent settling of black rot or grey mold on the patches they leave in their trail meaning leaves and flowers can get deformed.

It has been observed, that often especially during inducing the blossoms in orchids (which is done by dropping the temperatures) masses of mealybugs suddenly occur. Mealybugs are often found on spikes, buds or flowers, is the increased concentration of amino acids in these plant parts.

 

Managing Mealy, 

If the infestation with this pest is already severe, you might find mealybugs on almost all parts of the plant. They can also be found under pot rims, in boxes, clips, sticks, as well as on or under the greenhouse shelving, windowsills, and even curtains are sometimes invaded. They know how to make themselves at home. As the temperatures drop they often crawl deeper into the potting mix too, so it can be hard to know how far along your infestation really is.

Meaning that fighting mealybugs can be a long lasting “hobby”. They get mostly introduced by other plants or parts of other plants, but also can be blown in with wind from nearby infested plants, like NZ Flax and citrus trees.

Humans and pets can also spread them by handling plants and moving through greenhouses. In general mealybugs can be treated relatively well, as long as there’s no wax or wool present. So it is always best to inspect your orchids frequently so you can concentrate on the Crawlers. The treatments with insecticides should be repeatedly applied in intervals of 10 to 14 days. As a rule of thumb, the older the larvae / instar, the trickier they are to eradicate.

BioNeem or another leaf shine spray is known to do a good job, just remember that Phalaenopsis usually don’t cope with the oil, as well as some other Orchid genera!

Spraying with these products is best done, for the most effect, in higher temperatures as insects don’t hide away like they do in the cooler morning hours (and with this product bees and bumblebees usually aren’t effected or killed). Using a systemic insecticide like Groventive will attack the surface dwellers you can see, as well as the other crawlers that are as yet hiding where surface sprays alone cannot reach. We stock both these products online and in store.

UV-Lamps or blue sticky traps can also be used to catch the male mealybugs if they become evident.

Bioforce Limited is one of the NZ companies that offer biological control agents, I.e. predatory crawlers to fight against crawlers.  https://www.bioforce.co.nz/ 

As a side note, when identifying an infestation, the Australian ladybugs can also be confused for Long-tailed mealybug, however they move much quicker as they go for their “takeaways” and they aren’t too fussy about what’s on the plate!

* Stadium: Stage. The period of time between 2 successive molts or one of the successive principal divisions in the life cycle of an arthropod (e.g., egg, nymph, adult).

** instar - Developmental stage Instar is the name given to the developmental stage of an arthropod between molts. For example, after hatching from the egg and insect is said to be in its first instar. When the insect molts it is then a second instar and so on.

Instar can be used for insects undergoing complete and incomplete metamorphosis.

***ovoviviparous is with the egg developing into the first instar inside the bug, viviparous is developing a critter without an egg